Computer systems, including servers and storage subsystems, use significant amounts of power. As computing requirements and the associated power requirements continue to increase, users are looking for ways to pack more computing power into smaller spaces while at the same time saving money and conserving energy. For example, companies are migrating towards high density server applications or modular computer systems, such as server blades and server bricks, instead of conventional U-sized servers (a U is a standard unit of measure for designating the height in computer enclosures and rack cabinets where 1U equals 1.75 inches). The most compact conventional U-sized servers are 1U high and typically hold two processors meaning that a maximum of 42 servers with 84 processors can fit in a standard 42U server rack cabinet. With the high density servers such as server blades, a standard 42U server rack cabinet can generally hold up to 252 servers with 252 processors where each server typically has one processor but may have more than one processor.
Increasing the number of servers within a server rack cabinet requires large power supplies able to supply power to the servers. Because the initial powering of a server produces a large current spike or inrush current before the server settles down to steady-state operation, a power supply must be able to satisfy the steady-state load as well the larger inrush load. To decrease the number of power supplies in high density server applications, multiple servers typically share a common power supply. Therefore, the inrush current load for a common power supply increases by a factor of how many servers are powered by the common power supply. In order to not fail when the servers power up, the common power supply must be powerful enough to satisfy the combined inrush load of all the servers associated with the common power supply. Because the common power supply must be built to handle the combined inrush load of the servers to prevent a failure, the common power supply is overbuilt for the steady-state operation of the servers. This results in a costly and overbuilt power supply that while adequate to handle the inrush load is overbuilt for steady-state operation which is where the common power supply typically operates. Therefore, the power supply operates inefficiently during steady-state operation.
One way to avoid an overbuilt power supply is to employ a central controller that controls and sequences the powering of the servers in a high density server application. One approach utilizing a central controller involves the use of jumpers on the CPU board of the servers so that the central controller can distinguish between the servers. By being able to distinguish between the servers, the central controller powers the servers one at a time thereby reducing the total inrush load. Instead of having a large inrush load by powering the servers simultaneously, the central controller powers the servers one at a time so that the common power supply only has to satisfy the inrush load for one server. Once a server has powered up and settled into steady-state operation, the central controller powers the next server, repeating the process until all the servers are powered. Therefore, the common power supply generally does not have to handle the combined inrush load for all the servers associated with it and only has to handle the inrush load for one server and the combined steady-state load for all the servers associated with it. Thus, the power supply is not overbuilt to satisfy the combined inrush load and therefore not as costly. But the central controller is an added cost and creates a single point of failure for the high density server application. If the central controller experiences a failure, then the common power supply may experience a power spike due to combined inrush load of all the servers since there is no central controller to sequence power and the common power supply is not designed to handle the combined inrush loads. Or the servers may not power up due to there being no central controller to sequence power to the servers.